This invention relates to golf clubs of the type having iron heads for use on tees and fairways, and more particularly to an improvement in the performance of the clubs of a set in response to an off-center impact with a golf ball.
It is now well understood that although the golfer controls the swing of a golf club head, at impact the club head behaves as though it were a free mass having a particular velocity. Most of the energy of this mass is imparted to the ball in about half a millisecond, after which the ball compressed against the club face springs clear of it as it resumes its spherical shape.
Ideally, the center of impact between the club head and the ball is below the center of gravity so that the club head will twist downward during impact. This twisting increases backspin on the ball normally produced due to the loft of the club head.
To better understand the backspin normally produced on the ball, the club head should be visualized as a wedge driven between the ground and the ball, rather than as a mallet as used to strike a ball in croquet or polo. During the time the ball is in contact with the club head, the ball will tend to slide up the face of the club and friction imparts backspin which is opposite to the rotation the ball would have if it were rolling away from the golfer on the ground. Consequently, by the time the ball springs free of the club face, significant backspin has been imparted to the ball.
This backspin is desired in order to stop the ball from rolling forward on the ground once it alights, particularly when the ball alights on the green. By designing the club head so that the center of impact will normally be below the center of gravity, the twisting action referred to above is produced. Such twisting action adds to the backspin normally produced. However, the twisting action sometimes results in a vibration of the club head that is transferred through the shaft to "sting" the golfer's hands. Worse yet, any vibration that is set up in the club head also interfers with the normal flexing of the end of the shaft during impact. That flexing is desired because as the ball springs free of the club face, the flexed shaft straightens out to impact extra force to the ball.
It would be desirable to uncouple the twisting action of the club head from the shaft. Then any vibrations of the club head will not affect the flexing of the shaft. The club head would be allowed to twist more freely for greater backspin control. This control of backspin may be achieved for each stroke by raising or lowering the center of impact on the club face as required.